Soft pedal and no rear brake actuation after rear disc conversion?

[Reddzedd]

Hello,
I recently got around to installing my QuickPerformance Ford 9" rear into my Malibu, and all went well until I got around to the brakes.
I got all of the lines installed and bled the rear brakes, but I'm still getting a super soft and low pedal with little/no actuation of the rear brakes.
The car originally came with front disc/rear drum, and I haven't changed the master cylinder or the proportioning valve from stock. I've looked around online and people are saying the QP 9" comes with low drag calipers (identifiable by metric bleeders, which these have), that need a stepped master cylinder in order to work properly. Other people say you can get away with a disc/disc proportioning valve with the stock master cylinder. Some even say they changed nothing and haven't had any problems.
I have the disc/disc proportioning valve on the way, and then found out later about the master cylinder/low drag caliper situation.

Also, not sure if this is related, but the brake light is lit up on the dash now too, with the level in the master cylinder full.

Anyone run into a similar issue and can provide a solid solution? There are too many answers out there to tell what is right.
Thanks in advance!

 

[pagrunt]

Did you use one of these in place of the brake pressure switch in the prop valve?

Combination and Prop Proportioning Valve Bleed Bleeder Tool PV2 PV4 Tool | eBay

Performance Online's new Combination and Proportioning Valve Bleed Tool is designed to replace the warning light switch (white plug) on the proportioning valve during the brake bleeding process. After the bleeding process is finished, simply remove our PvBT Tool and reinstall the warning light...

www.ebay.com

 

[pontiacgp]

the proportioning valve probably needs to be reset

 

[Reddzedd]

the proportioning valve probably needs to be reset

I got the valve to reset and the light on the dash went out... but the pedal feels the same and the light comes back on after a few full pedal strokes, and I can hear the valve click.

Should I try bleeding it with the valve reset?

 

[fleming442]

I got the valve to reset and the light on the dash went out... but the pedal feels the same and the light comes back on after a few full pedal strokes, and I can hear the valve click.

Should I try bleeding it with the valve reset?

Absolutely. If you have enough air in the line to trip it, it will trip again- same as no fluid. Reset, gravity bleed, then pressure bleed. If you have the Seville calipers, they are a pain to bleed. They also need the e-brake cycled to ratchet the pistons out.

 

[olds307 and 403]

You may need a pressure bleeder. My 70 Cutlass had the exact same issue after changing the master cylinder, rear lines and wheel cylinders. Same low pedal and nothing would come out the rear. I pulled apart and checked the combination valve, in the proper position. I even swapped back in the old master cylinder, nothing. Motive Pressure bleeder instantly put fluid at the back. It is 4 wheel drum but same issue.

 

[Reddzedd]

Absolutely. If you have enough air in the line to trip it, it will trip again- same as no fluid. Reset, gravity bleed, then pressure bleed. If you have the Seville calipers, they are a pain to bleed. They also need the e-brake cycled to ratchet the pistons out.

Opted to get the rear discs without the parking brake. I reset the valve and bled that way, same thing; just trickled brake fluid from the rear calipers. I think I'll try like olds307 said and try to pressure bleed. If I still get nothing, I'll try again once the new prop valve comes in.

 

[Reddzedd]

Those who have pressure-bled their system, which bleeder/adapter did you use?

 

[fleming442]

Have a Motive with dried up hand pump seals. I suppose I could figure a way to do shop air, but it needs to be dry shop air.

 

[olds307 and 403]

I used a Motive 105 power bleeder. It would fit on the G body master cylinder as far as size, plenty big for the slightly smaller 70 master cylinder.